Four stroke cylinder multi-cylinder reciprocating internal combustion engines used in automobiles are capable of being operated over great speed and load ranges. Those skilled in the art have recognized for years that lower specific fuel consumption is usually achieved when an engine is operated at relatively high load. This is particularly true for spark ignition engines because throttling losses are minimized when the engine is operated at or near wide-open throttle at full load conditions. Unfortunately, in automotive usage, engines are frequently required to operate at less than maximum load. While an engine operates at part load, fuel economy suffers because of the pumping loss. Therefore, it is desirable to avoid partial load operation of the engine.
Engines have been designed that avoid part-load operation by deactivating some of the cylinder combustion chambers so as to allow the remaining active cylinders to be operated at higher loads. For example, it is noted to deactivate both the intake and outlet valves of one or more cylinders in an engine, which traps air in the deactivated cylinders. The trapped air is alternately compressed and expanded and acts as a pneumatic spring (See FIG. 3). This method of cylinder deactivation is highly efficient however, a small problem can occur at low pressures at bottom dead center piston position with oil pumping into the cylinder. More significantly, prior art systems which deactivate both the intake and exhaust poppet valves of an engine cylinder are quite expensive and are therefore unattractive because vehicles in which fuel economy is most important are frequently sold in a lower price range.
Stockhausen et al., U.S. Pat. No. 5,642,703 commonly assigned, provides an internal combustion engine wherein the operation of the intake and exhaust poppet valves are phase retarded in equal amount to produce valve lift events which are approximately symmetric with respect to the bottom dead and the top dead center positions of the piston motion, respectively. The phase retardation of the intake and exhaust poppet valves results in gas being expelled during the exhaust stroke back into the manifold to be reintroduced into the cylinder during the start of the intake stroke and gas being introduced into the cylinder at the end of the intake stroke being pushed back out of the cylinder during the start of the compression stroke. The engine of Stockhausen et al. has a slight pump working penalty. Additionally, controlling the transition between actuated cylinder condition and deactivated cylinder condition can sometimes be difficult. It is also difficult to determine the point of no net flow. Lastly, the internal combustion engine according to Stockhausen et al. requires increased exhaust valve to piston clearance (needs nearly a free wheeling engine) and a very wide range (90 degrees) cam retard phase shifter with rapid response is required.